Effect of Continuous-Flow Mechanical Circulatory Support on Microvasculature Remodeling in the Failing Heart.

Left ventricle (LV) unloading caused by a left ventricular assist device (LVAD) has been shown to enhance reverse LV remodeling in end-stage cardiomyopathy. Several reports consistently suggest that a pulsatile-flow LVAD has more profound effects compared to continuous-flow LVAD, though the responsible mechanisms are not fully understood. We hypothesized that arterial pulsatility, being affected by the type of LVAD, may affect microvasculature and functional/pathological LV remodeling in end-stage cardiomyopathy. The study included 18 patients with chronic heart failure who underwent LVAD implantation. Eight patients were implanted with pulsatile-flow LVAD, and 10 patients were implanted with continuous-flow LVAD. The results of serial echocardiograms and histopathological assessment of transmural LV tissues, which were collected during the implantation and removal of LVADs, were compared between the groups. The results of echocardiography showed that LV systolic dimension and LV ejection fraction improved greatly in the pulsatile-flow LVAD group compared to the continuous-flow LVAD group. Histological analysis showed that in both groups, increased microvasculature density and decreased cardiomyocyte size during LVAD support had no significant difference. In contrast, only the patients with continuous-flow LVADs had presented with significant increase in α-smooth muscle actin (α-SMA)-positive layer thickness and the number of proliferating cell nuclear antigen (PCNA)-positive cells of myocardial arterioles. We concluded that the use of long-term continuous-flow LVAD support, having less pulsatility, had induced more thickening to the medial layer of myocardial arterioles compared to the use of pulsatile-flow LVADs. Our findings suggest that the pathological impairment of myocardial microvascular structure during continuous-flow LVAD support may be a novel mechanism which accounts for the difference in LV remodeling depending on the type of LVAD.